Photonic crystals are periodic microstructures that affect the motion of photons that are incident upon the photonic crystals in a way that causes visual effects. These structures manipulate specific wavelengths of light, resulting in a visually varied or patterns of color. Unlike colored objects that contain chemical substances that reflect and absorb certain wavelengths of light to give the object a particular color, photonic crystals reflect color by its physical microstructures, and are therefore said to reflect color by “structural coloration.”
Examples of photonic crystal structures in nature include some butterfly wings that are brilliant iridescent blue due to microstructures within the butterfly wing. Photonic crystals can also be fabricated using stacks of dielectric layers of material or by forming two-dimensional patterns within a substrate. For example, two materials having different refractive indices arranged in very closely packed array patterns can create such photonic crystal effects. However, fabricated photonic crystals have fixed microstructures, and therefore have fixed responses to incident light and therefore have corresponding fixed colors.